A very interesting plot! I like the angle you've taken, focusing on how the protagonist - who fits the usual sidekick archetype - reacts to a new being in his world, let alone as part of his family. I found Josh's reactions to Kora very realistic in how he's quite wary at first and still retain some of it even as he gets to know her better.

Kora is very interesting as well. It's quite admirable how positive she tries to be in the wake of such a huge tragedy. I'm also curious as to how she really feels about her cousin and whether there is indeed another side to Leo (which I almost suspect will be starkly different to the good PR Josh noticed in the first chapter).

The writing style seems a bit simpler than your other stories, so I'm wondering if you are intentionally gearing towards a younger audience with this one. It makes it easy to read, though. I think maybe you should use less complex vocabulary than "unimaginably awful" when Josh is speaking. He sounds like he's still pretty young, and that kind of phrasing is something that would be more appropriate coming from someone older.

I think you should go ahead and make the story take place in Britain, or alternate-universe Britain. I'm an American, but I know terms like "mum", and phrase like "I'll be round in a tick" are very distinctly British. Leo in particular talks like she learned her vocabulary from some old-school British actress. There's not much need to have American-isms here.

A quick note: the story describes Kora as having black hair, but the picture shows her having slime-green hair. You might want to make sure the art and story are both working together.

Anyways, the general thrust of the story was easy to understand and get into. If you keep working on it, it will do quite nicely for your chosen audience.

I'm curious as to why you felt the need to rewrite the other story, especially when the main characters and plot are essentially the same. Josh being not as sweet in this version doesn't really translate too well because he is still more than accommodating to Kora, so perhaps writing in some specific examples through his speech and actions would make the difference more obvious. I'm also confused as to the parody side of the story. Besides from Leo's backstory being similar to Supergirl, I don't see the story as too much of a deliberate exaggeration of Supergirl, it's more of an homage or nod to the mythos. The black comedy bit is missing as well and I know this is still the first chapter but it would be best to implement different literary techniques as early in the story as possible to really differentiate it from the original.